1. Field of the Invention
This disclosure relates to printers utilizing a printing ribbon and, more particularly, to a ribbon tensioning assembly to be used for tensioning the ribbon in printers.
2. Description of the Related Art
Thermal transfer printers require adequate ribbon tension to assure proper feed of the ribbon to maintain the print quality on the print media. The tension on the ribbon prevents it from developing slack which can lead to wrinkling of the ribbon. Most printers provide a torquing mechanism to provide the tension in the ribbon supply roll. This structure is configured so that the tension force acting on the ribbon is a function of the radial distance from the center of the supply hub located at the center of the supply roll to the tangent point at which the ribbon leaves the supply reel.
The problem with this structure is that the tension force tends to be lower at the beginning of the roll and higher at the end of the roll. The ribbon on a full supply roll has a larger radial distance between the center of the roll and the tangent point at which the ribbon leaves the roll. Since torque remains substantially constant and the radius is relatively large, the tension force is small. As the ribbon is fed off the supply roll, the radius decreases resulting in an increased tension force in the ribbon.
Depending on the type of print media, it is desirable to sometimes use a ribbon of a different width. Wrinkling of ribbon is less of a problem for narrow width ribbons. Therefore, the tension force required is less for narrower ribbons and greater for wider ribbons. It would be advantageous to be able to adjust the tension of the ribbon to account for varied widths of ribbon.
Thus, a need exists for a ribbon tensioning assembly that provides an adjustable constant tension force to the ribbon regardless of the amount of ribbon on the ribbon supply roll. A need also exists for a ribbon tension adjustment in which tension can be varied to the ribbon based on the width of ribbon used. A need also exists for providing different tensions for various media and ribbon combinations.